This invention relates to the field of three-modulator projection display systems, more particularly to display systems using three digital micromirror devices (DMD(trademark)) and a color splitting prism assembly.
Digital micromirror devices are used to create very high quality images for a wide range of applications. DMD displays range from projectors using one DMD and sequential color methods that weigh less than five pounds, to large venue projectors used in cinematic applications. The large venue projectors use a set of color splitting prisms to separate a white light beam into three primary color light beams and direct the three primary color light beams to three separate modulators. The modulators each modulate a primary color light beam with image data of that primary. The color splitting prism assembly recombines the three primary color light beams into a full-color modulated light beam. The full-color beam is focused onto an image plane to produce the desired image.
A key design criteria for any image projector is the brightness of the projected image. Consumers demand very bright images that easily can be seen in spite of high ambient light levels. Even in display venues such as theaters where the ambient light levels are kept low, the ability to project very bright images enables the use of large display screens. Thus it is commercially advantageous to produce as bright an image as possible.
Projectors that produce very bright images utilize very powerful light sources. Unfortunately, at very high illumination levels, for example 10,000 lumens, the absorption of light by components of the illumination optics creates a tremendous amount of heat. Thus it is critical to minimize the amount of light absorbed by the illumination and projection optics, especially components such as the DMD that are directly in the path of the focused illumination beam. The highly reflective array of mirrors on the surface of the DMD limits the light absorbed by the DMD. The region of light outside the array of mirrors, however, absorbs light and gets very hot during operation of the display projector. The heat absorbed by the DMD limits the maximum power of the lamp used in the projection system and therefore is the limiting factor in projector brightness.
What is needed is a method of reducing the optical heating of the DMD in a projector to enable the use of larger projector lamps.
Objects and advantages will be obvious, and will in part appear hereinafter and will be accomplished by the present invention which provides a method and system for reducing the optical heating of a spatial light modulator by using a bandpass filter to reduce the thermal impact of dichroic light shift. One embodiment of the present invention provides a method of creating a full color image. The method comprising the steps of: providing a white light beam to a first prism, the white light beam entering a first face of the first prism and traveling to a second face of the prism, reflecting a first primary color portion of the white light beam and passing a first remainder portion through the second face of the first prism and a first face of a second prism, the reflected first primary color portion exiting the first prism through an exit face, modulating the first primary color portion, reflecting a second primary color portion of the first remainder portion at a second face of the second prism and passing a third primary color portion through a third prism, modulating the second and third primary color portions, focusing the first, second, and third modulated primary color portions onto an image plane, and further filtering at least one of the first, second, or third portions at an exit face of the first, second, or third prism.
A second embodiment of the disclosed invention provides a color splitting prism assembly comprising: a first prism, a second prism, a third prism, wherein a first dichroic filter at an interface between the first and second prisms reflects a first primary color component of a white light beam passing through the first prism, and a second dichroic filter at an interface between the second and third prisms reflects a second primary color component of a white light beam passing through the second prism, and an additional filter at an exit face of at least one of the prisms.
A third embodiment of the disclosed invention provides a dichroic prism comprising: a first face for admitting a beam of light, a second face for receiving the beam of light, a first filter formed on the second face, the first filter for reflecting a portion of the beam of light having a first band of wavelengths and for transmitting a second portion of the beam of light, a third face for receiving the reflected portion of the beam of light, and a second filter formed on the third face for transmitting the first portion of light and reflecting light substantially outside the band of the first portion of light.
The disclosed invention provides the technical advantage of preventing light modulated by a first primary color modulator from reaching a second modulator. The changed angle of the modulated light causes a portion of the modulated light to react differently with a dichroic filterxe2x80x94passing through the filter on a second pass when the light was reflected by the filter on a first pass, or vise-versa. If this stray light reaches a second modulator, it will be absorbed by the non-active portions of the second modulator and heat the second modulator. Placing an additional filter on or near the exit face of a prism associated with the second modulator prevents the light modulated by a first modulator from reaching the second modulator and thus reduces the temperature of the second modulator.